Previously, nucleating agents have been used for various applications in a silver halide photographic materials. For example, hydrazines which have been used widely as nucleating agents have been used in direct positive internal latent image-forming silver halide emulsions and have been used for increasing sensitivity and/or gradation in negative type surface latent image-forming silver halide emulsions.
Direct positive photography includes various methods. Such methods include the method of exposing silver halide grains which have been fogged in advance in the presence of a desensitizer followed by their development and the method of exposing silver halide grains having photosensitive nuclei mainly inside the grains followed by their development in the presence of a nucleating agent. The present invention relates to the latter method. In this respect, silver halide emulsions having photosensitive nuclei mainly inside the silver halide grains and which form latent images mainly in the inside of grains are referred to as an internal latent image type silver halide emulsion and should be distinguished from silver halide grains which form latent images mainly on the surface of grains.
Methods for obtaining positive images directly by surface development of an internal latent image type silver halide photographic emulsion in the presence of nucleating agent, as well as photographic emulsions and photosensitive materials used in such methods, have been disclosed in, for example, U.S. Pat. Nos. 2,456,953, 2,497,875, 2,497,876, 2,588,982, 2,592,250, 2,675,318, 3,227,552, and 3,317,322, British Patents 1,011,062, 1,151,363, 1,269,640, and 2,011,391, Japanese Patent Publication Nos. 29405/68 and 38164/74, and Japanese Patent Application (OPI) Nos. 16623/78, 137133/78, 37732/79, 40629/79, 74536/79, 74729/79, 52055/80, and 90940/80 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
The nucleating agent may be added to the developing solution in the above-mentioned method to obtain a positive image directly. In addition, nucleating agents may be added to photographic emulsion layers or other appropriate layers in a photosensitive material.
Of the suitable nucleating agents which have been added to a silver halide photosensitive materials, hydrazine compounds have been frequently used. As specific examples of such nucleating agents, there are those nucleating agents disclosed in Research Disclosure, RD No. 23510 (November, 1953), RD No. 15162 (November, 1976, Vol. 151), and RD No. 17626 (December, 1978, Vol. 176). In general, hydrazine-containing nucleating agents have large differences between their maximum densities (Dmax) and their minimum densities (Dmin) and have been found to be superior with respect to discrimination. However, they have a drawback in that high pH values (i.e., higher than 11) are necessary for treatment. As nucleating agents which are capable of functioning at low pH values (i.e., not higher than 11), heterocyclic quaternary ammonium salts have been used. Examples of these can be found in U.S. Pat. Nos. 3,615,615, 3,719,494, 3,734,738, 3,759,901, 3,854,956, 4,094,683, and 4,306,016, British Patent 1,283,835, and Japanese Patent Application (OPI) Nos. 3426/77 and 69613/77. In particular, propargyl- or butynyl-substituted heterocyclic quaternary ammonium salt compounds such as those mentioned in U.S. Pat. No. 4,115,122 are excellent nucleating agent with respect to discrimination in direct positive silver halide emulsions. However, in silver halide emulsions, and in particular, color photosensitive materials, when a sensitizing dye is used with the aim of spectral sensitization, a competitive adsorption occurs between the sensitizing dye and the heterocyclic quaternary ammonium-containing nucleating agent. As a result, since quaternary ammonium-containing nucleating agents have weak adsorbing properties, it has been necessary to add a large amount of the nucleating agent. Therefore, with multilayer color photosensitive materials, the use of large amounts of nucleating agents sometimes results in an unevenness of density or in loss of color balance. Furthermore, the nucleating agent has been found to exhibit insufficient performance. In an effort to overcome this problem, quaternary ammonium salt-containing nucleating agents having thioamide groups for promoting adsorption on AgX were developed and disclosed in U.S. Pat. No. 4,471,044. In particular, it was disclosed that the amount of nucleating agent which is necessary to obtain sufficient Dmax is reduced. Also, the reduction in Dmax with time at high temperatures is improved by introducing a difference in adsorption. However, even with these improvements, the effect of these nucleating agents have not been sufficiently satisfactory.
Furthermore, it is known to improve various photographic characteristics by using a nucleating agent in a negative type surface latent image-forming silver halide photographic material. For example, it is known that a negative image of high contrast having a large gamma value (i.e., of 10 or more) can be obtained by processing a surface latent image type silver halide negative emulsion with a processing solution having a high pH (i.e., 11 or more) in the presence of a hydrazine-containing nucleating agent. This is discussed in U.S. Pat. Nos. 2,419,975, 4,224,401, 4,168,977, 4,243,739, 4,272,614 and 4,323,643. Examples of hydrazine-containing nucleating agents having a group for promoting adsorption on silver halide grains are disclosed in U.S. Pat. Nos. 4,385,108 and 4,269,929. Furthermore, it is known that increased sensitivity can be obtained by processing the combination of a negative emulsion and a hydrazine compound at a low pH (i.e., not higher than 11).
It is also known that quaternary ammonium salt-containing compounds act to promote development in a silver halide negative emulsion-containing photosensitive material. This is discussed, for example, in U.S. Pat. No. 4,135,931, Japanese Patent Application (OPI) Nos. 114328/77 and 121321/77, West German Patent 2,647,940, and Belgian Patent 721,658.
However, the use of the nucleating agents discussed above has been found to necessitate an increase in an amount of nucleating agent which is added to achieve a sufficient effect and the effect is largely dependent on the particular processing method used.
It is known that a direct positive photosensitive material provides a re-reversal negative image in the region of a large amount of light and it is also known that when a direct positive photosensitive material is exposed for a short time at high illumination (high illuminance exposure) or is exposed for a long time at low illumination (low illuminance exposure), the re-reversal negative image is liable to appear at the former exposure in comparison with the latter exposure provided that the amount of light is the same. Therefore, it has been desired to provide a direct positive photosensitive material which minimizes the formation of the re-reversal negative images at high illuminance exposure.
Further, it has also been desired to provide a direct positive photosensitive material which shows reversal effect in the initial stage of development exposure (e.g., 40 sec. or 60 sec. development).